1. Field of the Invention
The present invention relates to a reforming apparatus, for use in a fuel cell, which reforms raw fuel into a reformed gas used in a fuel cell system.
2. Description of the Related Art
A polymer electrolyte fuel cell produces electric power by converting chemical energy of hydrogen into electric energy. For practical purposes, the hydrogen used as a fuel for the polymer electrolyte fuel cell is obtained in a manner that a hydrocarbon-based gas, such as natural gas or naphtha relatively easily procurable at a relatively low cost, or a raw fuel gas of an alcohol type, such as methanol, and steam are mixed together and then reformed by a reformer. The hydrogen gas obtained by the reforming is supplied to a fuel electrode of the fuel cell and used to generate electricity.
Generally, steam required for the reforming in the reformer can be obtained by conducting heat exchange between a combustion exhaust gas and a fuel gas discharged from the reformer. However, when water of low temperature is rapidly heated by conducting heat exchange, there are cases where the flow rate of steam varies significantly due to the pulsating movement of partially boiled water. Such a state causes the mixture ratio of steam and raw fuel gas (steam-carbon ratio (S/C ratio)) to vary, which hinders the stabilized generation of hydrogen gas in the reformer and consequently contributes to the hindrance of the stabilized supply of hydrogen gas to a fuel cell stack.
In order to suppress the variation in the flow rate of steam caused by the water boiling, a fuel reforming apparatus is designed such that a means for narrowing down the feed water is provided between a carbon monoxide remover and a steam generator in a feed-water heating line through which the feed-water is introduced into the steam generator (See Patent Document 1, for instance)
[Patent Document 1] Japanese Unexamined Patent Publication No. 2002-241108.